This invention relates to transceivers and in particular though not exclusively to FMCW transceivers operable in the millimeter wavelength band.
Presently the difficulty of providing good transmit and receive channel isolation for monostatic CW radars becomes further aggravated at high frequencies (millimeter waveband) due to the poor performance of circulators which are the basis of the conventional approach.
One method of providing separate channels with an "in principle" infinite isolation, is to use the ability of a suitably dimensioned waveguide (usually square or circular) to support two independent crossed polarizations. However, if the transmit and receive beams are simply crossed linear polarizations, poor performance results due to an effective loss of target echo.
Much of this loss can be retrieved by using crossed circular polarization. A scheme of this nature is proposed in "Applications of the Turnstile Junction" by Meyer and Goldberg, IRE Transactions MT and T December 1955 using the properties of the "Turnstile Junction". This scheme does not, however, conveniently permit the use of balanced mixers which are essential for good overall sensitivity.
There is a requirement for a simple low cost miniaturized FMCW microwave system.